Black cabbage tree  (Melanodendron integrifolium)

Classified as Vulnerable (VU) on the IUCN Red List (1).

The black cabbage tree is a fairly large, spreading tree whose rough bark is permanently moist and is often darkened by a dense layer of mosses, lichens and ferns (2) (3). The smooth, dark leaves are thick and fleshy, and grow clustered towards the end of the branches, somewhat resembling cabbages and so giving this tree its common name (2) (3) (4). The leaves are quite large and leathery, and roughly oblong in shape, wider at the base, with entire (non-toothed) margins (4) (5).

The black cabbage tree is endemic to the island of St Helena, where it has a patchy distribution on the central ridge between 580 and 820 metres above sea level. Around 800 specimens are found across Diana’s Peak National Park, with smaller numbers at High Peak and one or two at Depot (1) (2) (3).

The black cabbage tree is a characteristic species of damp areas on mountain slopes, where it is particularly associated with tree-fern (Dicksonia) thicket (1) (6).

The black cabbage tree blooms in October and November, bearing clusters of daisy-like flowers on the ends of the branches, surrounded by the leaves (2) (3). Each ‘flower’ measures around 1.2 centimetres across (2) (3), and, like other members of the Compositae family, is in fact a compound structure composed of many tiny, individual flowers known as florets (7). The ‘flower’ of the black cabbage tree is made up of around 60 to 75 central, yellowish disc florets surrounded by 20 to 25 white, petal-like ray florets (4) (5).

The seeds of the black cabbage tree often germinate on the trunks of tree-ferns, the weight of the black cabbage tree eventually causing the tree-fern to fall. The tree-fern and the cabbage tree both then continue to grow, the cabbage tree often rooting into the soil (1) (2) (3) (6).

Since St Helena was first settled by humans, the native vegetation has been almost entirely destroyed by introduced grazers, cutting for timber and fuel, clearance for cultivation and plantations, and introduced plants. The remaining natural vegetation is now confined to the central mountain peaks (6) (7) (8). Although considered the most abundant of the endemic cabbage trees on St Helena, only a thousand or so black cabbage trees are thought to remain, and occur only in a few, fragmented locations (1) (9). The main threat to this species is competition from the introduced New Zealand flax (Phormium tenax), as well as other invasive exotic species such as Buddleia madagascariensis and Fuchsia coccinea, which have spread into and overrun the remaining areas of tree-fern thicket (1) (6) (8).

The black cabbage tree is protected within Diana’s Peak National Park, which has been subject to a management plan since 1996 in recognition of the great biological interest of the tree-fern thicket (1) (8). The black cabbage tree is also a protected species in St Helena under the Endangered Endemic and Indigenous Species Protection Ordinance No 7 of 1996 (1). Work has been underway to rescue the remaining areas of tree-fern thicket by eradicating invasive exotic plants such as flax, and by restocking plant populations with nursery-raised seedlings and cuttings (1) (3) (8). Although long-term storage of black cabbage tree seed does not seem possible because of the relatively short period the seeds remain viable (1) (3), the survival rates of transplanted seedlings appears to be good, and the population of this unusual tree, although still dependent on conservation management, is now increasing (1).

To find out more about conservation on St Helena see:

• St Helena National Trust:
  http://www.nationaltrust.org.sh
• Joint Nature Conservation Committee (JNCC) - St Helena:
  http://www.jncc.gov.uk/pdf/ot_sthelena.pdf